Most LCD devices are passive devices in which images are displayed by controlling an amount of light input from an outside light source. Thus, a separate light source (for example, backlight module) is generally employed for illuminating an LCD.
Generally, backlight modules can be classified into an edge type or an edge type based upon the location of lamps within the device. The edge type backlight module has a lamp unit arranged at a side portion of a light guiding plate that guides light. The edge type backlight modules are commonly employed in small-sized LCD due to their lightweight, small size, and low electricity consumption. However, the edge type backlight modules are not suitable for large-sized LCD (20 inches or more). An edge type backlight module has a plurality of lamps arranged in regular positions to directly illuminate an entire surface of an LCD panel. The edge type backlight modules have higher efficiency of light usage and longer operational lifetime than the edge type backlight modules, the edge type backlight modules are especially used in large-sized LCD devices. However, an LCD device usually employs a significant amount of lamps to reach a high luminance. The significant amount of lamps results in a great deal of heat produced and cumulated inside the LCD device. Therefore, heat dissipation of the edge type backlight modules is usually a hard nut to crack.
Referring to FIG. 9, a typical direct type backlight module 100 is shown. The backlight module 100 includes a frame 110, a diffusion plate 120, a heat dissipating plate 130, a reflective plate 140, and a plurality of lamp tubes 150. The frame 110 includes a base 112 and four sidewalls 114 that extend from the peripheral of the base 112, the base 112 and the sidewalls 114 cooperatively define a chamber 116. The heat dissipating plate 130 is disposed on the base 112 of the frame 110. The reflective plate 140 is positioned on the heat dissipating plate 130. The lamp tubes 150 are aligned in the chamber 116 above the reflective plate 140. The diffusion plate 120 is disposed on the frame 110 covering the chamber 116. The reflective plate 140 is used to reflect a part of light rays emitted from the lamp tubes 150 to the diffusion plate 120. The diffusion plate 120 is used to diffuse or reflect light rays by means of shielding, scattering, or refraction.
In order to decrease heat that reduces lifetime of the lamp tubes 150 and causes distortion of the diffusion plate 120 from accumulating in the chamber 116, the bottom surface of the base 112 defines a plurality of fin structures 118 thereon. Heat is efficiently dissipated out from the fin structures 118 via the heat dissipating plate 130. However, the thickness of the backlight module 100 is limited due to the physical properties of the frame 110. In addition, in order to enhance uniformity of light rays for the backlight module 100, there must be a big space between the diffusion plate 120 and the lamp tubes 150 for eliminating potential dark strips caused by the reduced intensity of light between adjacent lamp tubes 150. Therefore, the backlight module 100 suffers from increased thickness and decreased luminance due to exiting between the diffusion plate 120 and lamp tubes 150.
What is needed, therefore, is an edge type backlight module that overcomes the above mentioned shortcomings.